Reciprocating piston pumps such as triplex pumps are well known in the art. Such pumps commonly employ a linkage including a crankshaft attached at one end to a rotating drive wheel or gear and at the other end to a crosshead slideably engaged in a lateral guide for converting the rotary motion of a drive into reciprocal motion of the crosshead. The crosshead is then connected to a pump piston or plunger via appropriate smaller diameter connecting rods. As is well known, longitudinal alignment of the pump linkage is critical for extended operation of the pump since any misalignment imposes friction and flexure stresses particularly in the connecting rods.
Over time even in closely aligned pumps, the linkage will eventually fail. It is hypothesized that stresses due to the constant reciprocation against pressure cause gradual hardening and embrittlement of the rods until one of them fails by breaking in two. While a periodic downtime for replacement of the broken rod is expected, the broken rod can sometimes result in damage to other components of the pump assembly. In addition, replacement of a broken rod can become difficult if substantial disassembly of the pump is required. Further, if the broken rod is an integral part of another component of the linkage (such as the crosshead), it may also be necessary to replace an expensive pump component which is otherwise in good condition.
Thus, there is a need for a pump linkage adapted to fail predictably. The linkage upon failure should not damage other components and be easily repaired with minimum downtime.
U.S. Pat. No. 4,566,370 to Hanifi discloses a reciprocating piston pump driven by a rotating drive via a crankshaft including a crosshead, a transfer rod and a piston. The connection between the transfer rod and the piston is said to ensure a certain lateral and angular moveability so as to avoid any distortion or twisting forces which could otherwise result in misalignment of the piston, crosshead and transfer rod.
U.S. Pat. No. 1,037,840 to Wintzer discloses a reciprocating piston in a cylinder driven by a rotating driver via a crankshaft, crosshead and piston rod.
U.S. Pat. No. 3,276,390 to Bloudoff et al. discloses a reciprocating pump driven by a rotating driver. A plunger is connected to a plunger mandrel by a bolt having a reduced cross section. The mandrel has a flange which is attached to a flange of an intermediate rod by a clamp wherein the intermediate rod is threadedly engaged to a crosshead. It is stated that under excessive loads breakage will occur at the bolt. Further damage which can occur on continued stroking is said to be limited to parts which are relatively inexpensive and easily replaceable.
U.S. Pat. No. 1,557,222 to Warner discloses a reciprocal pump apparatus powered by a rotating drive wheel having an eccentrically attached crankshaft. The crankshaft is pivotably connected to a reciprocating crosshead which, in turn, is connected to a piston rod. The crosshead rides in a cross guide and a threaded end of the piston rod engages a threaded bore in the crosshead.